High temperature rabble design

ABSTRACT

Rabble life, e.g., in rotary hearth coke calciners, is greatly extended by welding grids, e.g., hexsteel honeycomb onto at least the wear surfaces of the rabbles and filling the honeycomb in with wear-resistant high temperature insulating cement.

[ June 19, 1973 United States Patent [1 1 Oleszko [54] HIGH TEMPERATURE RABBLE DESIGN 3,594,286 7/1971 Kemmerer, 202/102 3,106,756 10/1963 249/199 Demaison...,.......................

Inventor: Thaddeus J. Oleszko, l-loechster Str.

7, 8263 Burghausen, Germany Dec. 2, 1971 Appl. No.: 204,102

Primary Examiner-John J. Camby [22] Filed:

Attorney-Joseph C. Herring, Richard C. Willson, Jr. and Jack L. Hummel ABSTRACT US. Cl. 259/66, 432/139 [51] Int. F27b 9/16 [58] Field of Search 263/26; 259/66;

Rabble life, e.g., in rotary hearth coke calciners, is

greatly extended by welding grids, e.g., hexsteel honey- 29/5301 29; 202/102 103, 104 comb onto at least the wear surfaces of the rabbles and filling the honeycomb in with wear-resistant high temperature insulating cement.

References Cited UNITED STATES PATENTS 2,317,941 Rowen..........,....,........ 263/26 X 6 Claims, 7 Drawing Figures I "an" Patented June 19, 1973 3,740,184

4 Sheets-Sheet 1 Patented June 19, 1973 3,740,184

4 Sheets-Shoot 2 Patented June 19, 1973 4 Sheets-Sheet 4 1 HIGH TEMPERATURE RABBLE DESIGN CROSS REFERENCES TO RELATED APPLICATIONS The following United States Patent applications relate to the general field of the present invention: Ser. No. 887,450 filed Dec. 22, 1969, (docket 680058- A-USA) and Ser. No. 888,698, filed Dec. 29, I969 (docket 680050- A-USA).

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION General Statement of the Invention According to the invention, a rabble (also called a plow) which is fitted with an inner cooling chamber or with a cooling conduit either of which is used for the circulation of cooling fluids, is protected on at least a portion of its external surface by welding or similarly fastening on an open grid which is then filled in with thermally insulating cement. The inner plow is preferably made of steel, titanium, or other similar metal. The cooling device will generally be an internal chamber or a U-shaped or other flat coil for the circulation of cooling fluids which can be either gases or liquids, most commonlyair or waterf'lhe grid can be a honeycomb, steel mesh or similar material which can be tightly atfixeti to the surface of the interior metal plow. The cement should be thermally insulating and is preferably abrasion resistant. In most instances, sufficient cement will be spread over the grid to completely fill it in and to completely cover it, protecting it from contact with the hot granular material to be moved by the finished rabble.

Utility of the Invention As discussed above, the invention finds particular utility in the movement of granular materials over the surface of rotary hearth furnaces, although it can alternatively be used for plowing materials across the surfaces of other materials handling devices, e.g., vibratory conveyors, Mannheim furnaces (in which the rabbles rather than the hearth generally move), and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation section view of a rotary hearth furnace suitable for use with the rabbles of the present invention.

FIG. 2 is a cross sectional view of the rotary hearth furnace of FIG. 1 showing details of the rabbles in place for moving material on the hearth.

FIG. 3 is a cross sectional view through the rabble pit of the furnace of FIG. 1 showing additional details of the rabbles of the present invention.

FIG. 4 is a schematic diagram showing the position ing of the rabbles of the present invention so as to move the material in windrows progressively across the rotating hearth of FIG. 1. i

FIG. 5 is a detail view taken at right angles to FIG. 3 and showing a single rabble according to the present invention.

FIG. 6 is an additional view showing the cooling chamber and baffle within a rabble of the present invention.

FIG. 7 is a perspective view of a stainless steel rabble of the present invention showing the hexagonal grid in place before it is filled in with cement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Furnace: Referring to FIGVI, the rotary hearth 10 has an inner hearth surface 11 sloping from the outer periphery downwardly to a central axially extending soaking pit 12 integral with and depending from the hearth 10. The rotary hearth 10 is supported on spaced rollers 13 mounted on a furnace frame 14 and is driven by a motor and a rack and pinion drive in conventional manner for rotary hearth furnaces. A curb 15 extends vertically above the hearth surface 11 at its outer periphery and carries a trough 16 with sand 17. A liquid may be used instead of sand, if preferred.

The furnace frame 14 carries roof beams 20 which support a refractory roof 21 having a central flue 22. The roof 21 has a depending wall 23 carrying flange 24 which extends into the sand 17 carried in trough 16 forming a rotary sand seal between the roof 2] and hearth 10. The roof 21 is provided with air ports 25 re ceiving air from duct 26 mounted on the furnace frame 14. The ports 25 direct air downwardly towards the hearth. Sidewalls 23 of the roof are provided with ports 27 receiving air from duct 28 also mounted on the frame 14. The ports 27 direct air generally across the hearth in a radial direction. Burners 2.9 are provided in the roof to bring the furnace to operating temperature and to provide additional heat for those reactions which are not completely autogenetic. A feed chute 30 passes through the roof 21 adjacent the sidewall 23 and is provided with a vertically adjustable delivery end 31 extending to a point adjustably selected to deliver a selected thickness of feed onto hearth surface 11. A radially extending U-shaped rabble pit 32 is formed in the roof from the flue 22 to the roof wall 23. The bottom of the pit 32 is provided with slots 33 adapted to slidably receive rabbles 34. Rabbles 34 may be solid or of hollow plate-like structure with inner vertical baffles 35, depending upon the temperature involved. For the higher temperatures, of course, the latter is preferred. Each baffle is provided with inlet 36 and outlet 37 coolant conduits which also act as supports for the rabbles. Coolant, such as water or air, is delivered to the inlet 36 and into rabble 34 on one side of the baffle 35 and then under baffle 35 to the opposite side of the rabble and out through outlet pipe 37. Refractory seals 38 are provided on conduits 36 and 37 to fit within slot 33. The conduits 36 and 37 are held between two angular rabble holders 39 and 40 which are held together by bolts 41. The rabble holders 39 and 40 are fastened between adjustable carrier angle beams 42 and 43 by bolts 44. Vertical adjustment screws 45 are provided at each end of each adjustable carrier beam 42 and 43. These screws 45 bear on fixed rabble beams 46 and 47 which extend across the rabble pit 32 as shown in FIG. 3. (Minor elements 35,39,40,4l,43,44 and 47 are not shown but have the configurations shown in connection with those element numbers in the aforementioned U.S. Pat. No. 3,475,286. These elements could have other conventional configurations.)

FIG. 7 shows a rabble partially covered with 1" type 316 stainless steel honeycomb 90 which is butt-welded in place over the principal contact surface of the hollow carbon steel internal plow 34 to which are connected coolant inlet conduit 36 and outlet conduit 37. For ease in fabrication k inch hexsteel 316 stainless steel honeycomb is used on the edge, bottom, and rear surface of the rabble. The honeycomb is then filled in with high temperature ceramic Plibrico-Precast 37 or Ramtite cement which is trowled over the honeycomb so as to cover it to a depth of approximately 1 inch and then permitted to set. This cement has a relatively high I thermal insulating coefficient and is tightly held by the hexsteel which also serves to provide internal reinforcement against tensile stresses in the cement.

A rotary discharge table 50 is provided beneath the soaking pit 12 to receive the output of such pit. A fixed discharge spout or plow 51 is mounted in frame 14 between the soaking pit 12 and discharge table 50. The spout 51 is provided with a peripheral trough 52 carrying sand 53 into which a depending flange 54 on the soaking pit extends to form a sand seal.

The operation of the furnace described above is as follows. The burners 29 are fired to bring the furnace up to the desired temperature which depends upon the nature ofthe material being devolatilized or calcined. Material to be devolatilized or calcined is fed through feed chute 30 and is continuously spread to the desired thickness and width along the outer periphery of hearth surface 11. As the hearth rotates, the material encounters the rabbles 34. Each set of rabbles deflects material striking it into the next adjacent concentric ring of the sloping hearth surface so that the flow of material from the periphery of the hearth surface 1 1 to the soaking pit 12 is generally in spiral concentric rings, each of greater width so that as the rings become smaller the area becomes greater, providing a uniform depth. These concentric spiral rings are diagrammatically illustrated in FIG. 4 together with the relative position of each rabble with respect to such rings. The vertical position of the rabbles determines the residual amount of material which is to be left on each ring as the hearth rotates. The rabbles tend to cause mixing and inversion of the bed several times as the material moves downwardly from the hearth periphery to the soaking pit. This permits more uniform heating and reaction and provides a more uniform product and is an important attribute of this invention.

When rabbles of conventional steel design similar to those shown in the aforementioned U.S. Pat. No. 3,475,286'are replaced with rabbles according to the present invention, the temperature of the cooling water (flowing at the same rate) at the rabble outlet drops 60C., from I C. to 50C., while the furnace interior is operating at an arch temperature of 1,400C. This difference in cooling water temperature reduces the cooling water requirement, permitting a substantial capital saving in cooling tower and related water handling equipment, but more importantly very valuable heat (temperature) is not removed from the coke. Furthcr, the rabbles made according to the present invention operate in substantially continuous service for more than 12 months, whereas previous conventional rabbles installed in the same position in the same fur nace had eroded sufficiently that they required replace ment in less than 3 months.

Modifications of the Invention rabble, it is possible to have flat quadrangular rabbles or other configurations to provide various patterns of arrangement of the particles of material upon the hearth. Various cements and castable materials can be used to coat the rabbles of the present invention, so long as the material is plastic and can be hardened with time or upon the application of heat or both, to form a surface which is resistant to the high temperatures to which the rabble will be exposed during use and so long as the material has a comparatively low coefficient of heat transfer. The Plibrico Precase 37 or plastic Ramtite material which is illustrative of the types of cements and castables to be used, can be dried and fired prior to installation on the furnace or can be installed after drying and fired in place on the furnace if desired.

What is claimed is:

1. A rabble for moving hot granular material disposed upon a substantially flat surface, said rabble comprising in combination:

a. a metal interior structure having cooling means for circulating a cooling fluid in heat transfer contact with said metal structure,

b. an open grid of metal affixed to said metal interior structure so as to cover at least a portion of the exterior surface thereof and,

c. a settable, thermally-insulating ceramic material at least partially filling open spaces in said grid whereby said internal metal structure is maintained at a substantially lower temperature than that of said hot granular material.

2. A process for the construction of a rabble for the movement of hot granular material lying on a substantially flat, substantially horizontal surface, comprising in combination the steps of:

a. fabricating an internal metal structure having generally rabble-like shape and having cooling means in heat transfer contact with said rabble-shape,

b. appending to said internal metal structure a metallic grid having open spaces and,

c. placing a plastic, settable thermal insulation within said open spaces of said grid, and

d. permitting said settable thermal insulation to set within said open spaces of said grid.

0 3. A rabble according to claim 1 wherein the grid of metal is fashioned from intersecting strips of metal lying in a plane substantially perpendicular to the plane of the exterior surface of said rabble so as to form a honeycomb grid. I

4. A rabble according to claim 3 wherein said honeycomb grid is fastened to the exterior surface of said rabble by welds.

5. A rabble according to claim 1 wherein said thermally-insulating ceramic material is a Ramtite ceramic material.

6. A process according to claim 2 wherein said rabble is installed in a rotary hearth furnace in materialstransfer contact with a bed of granular material lying on the surface of a rotating circular hearth. 

1. A rabble for moving hot granular material disposed upon a substantially flat surface, said rabble comprising in combination: a. a metal interior structure having cooling means for circulating a cooling fluid in heat transfer contact with said metal structure, b. an open grid of metal affixed to said metal interior structure so as to cover at least a portion of the exterior surface thereof and, c. a settable, thermally-insulating ceramic material at least partially filling open spaces in said grid whereby said internal metal structure is maintained at a substantially lower temperature than that of said hot granular material.
 2. A process for the construction of a rabble for the movement of hot granular material lying on a substantially flat, substantially horizontal surface, comprising in combination the steps of: a. fabricating an internal metal structure having generally rabble-like shape and having cooling means in heat transfer contact with said rabble-shape, b. appending to said internal metal structure a metallic grid having open spaces and, c. placing a plastic, settable thermal insulation within said open spaces of said grid, and d. permitting said settable thermal insulation to set within said open spaces of said grid.
 3. A rabble according to claim 1 wherein the grid of metal is fashioned from intersecting strips of metal lying in a plane substantially perpendicular to the plane of the exterior surface of said rabble so as to form a honeycomb grid.
 4. A rabble according to claim 3 wherein said honeycomb grid is fastened to the exterior surface of said rabble by welds.
 5. A rabble according to claim 1 wherein said thermally-insulating ceramic material is a Ramtite ceramic material.
 6. A process according to claim 2 wherein said rabble is installed in a rotary hearth furnace in materials-transfer contact with a bed of granular material lying on the surface of a rotating circular hearth. 